OFDM系统信道盲估计的一种新算法

利用循环前缀（CP）引入的信息冗余，在利用接受信号的二阶统计特性实现正交频分复用（OFDM）系统信道盲估计的子空间算法基础上，采用矩阵变换的方法，改善信息序列的非周期相关函数，推导出信道估计的新算法。     

降低雷达接收机中噪声的几种方法

噪声是影响雷达接收机灵敏度的重要因素。本文通过讨论雷达接收机噪声的来源，分析并提出了集中降低雷达接收机内部和外部噪声的几种方法，具有一定的实际意义。     

基于AutoCAD2000的图解法确定工艺转角

提出了基于AutoCAD2 0 0 0的图解法求解机械加工过程中工艺转角的问题 ,并针对具体的应用实例给出了圆满的解答 ,并验证了其精度。     

Wavelet based Denial-of-Service detection

Network Denial-of-Service (DoS) attacks that disable network services by flooding them with spurious packets are on the rise. Criminals with large networks (botnets) of compromised nodes (zombies) use the threat of DoS attacks to extort legitimate companies. To fight these threats and ensure network reliability, early detection of these attacks is critical. Many methods have been developed with limited success to date. This paper presents an approach that identifies change points in the time series of network packet arrival rates. The proposed process has two stages: (i) statistical analysis that finds the rate of increase of network traffic, and (ii) wavelet analysis of the network statistics that quickly detects the sudden increases in packet arrival rates characteristic of botnet attacks.Most intrusion detections are tested using data sets from special security testing configurations, which leads to unacceptable false positive rates being found when they are used in the real world. We test our approach using data from both network simulations and a large operational network. The true and false positive detection rates are determined for both data sets, and receiver operating curves use these rates to find optimal parameters for our approach. Evaluation using operational data proves the effectiveness of our approach.     

阶跃信号突变点检测的小波分析法

文章运用小波理论这种新的数学工具,对于由基本平稳的慢变信号和阶跃型突变信号线性组合而构成的这类信号,提出了一种以连续小波变换为主体的检测和分析方法。理论以及实例分析表明,这种方法对于阶跃型突变信号的检侧,是颇为有效的。     

Ultrahigh-performance FFTs for the CRAY-2 and CRAY Y-MP supercomputers

In this paper a set of techniques for improving the performance of the fast Fourier transform (FFT) algorithm on modern vector-oriented supercomputers is presented. Single-processor FFT implementations based on these techniques are developed for the CRAY-2 and the CRAY Y-MP, and it is shown that they achieve higher performance than previously measured on these machines. The techniques include (1) using gather/scatter operations to maintain optimum length vectors throughout all stages of small-to medium-sized FFTs, (2) using efficient radix-8 and radix-16 inner loops, which allow a large number of vector loads/stores to be overlapped, and (3) prefetching twiddle factors as vectors so that on the CRAY-2 they can later be fetched from local memory in parallel with common memory accesses. Performance results for Fortran implementations using these techniques demonstrate that they are faster than Cray's library FFT routine CFFT2. The actual speedups obtained, which depend on the size of the FFT being computed and the supercomputer being used, range from about 5 to over 300%.     

基于小波包和包络分析的滚动轴承故障自动诊断方法

提出了一种基于峭度-小波包-包络分析的滚动轴承故障自动诊断方法。首先用峭度系数判断是否出现故障,再针对故障轴承振动信号非平稳和调幅的特点,用小波包将信号分解到不同的节点上。然后将不同节点的重构信号做包络谱分析,将谱峰处的频率同滚动轴承内圈、外圈、滚珠、保持架等的故障频率进行对比分析,在此基础上,运用最小距离判别法则自动获得故障原因,从而实现滚动轴承故障的自动诊断。通过对实验中采集到的轴承振动信号进行分析,证明了该方法在轴承早期故障诊断中的有效性。     

DC-DC电荷泵的研究与设计

以Dickson电荷泵的基本原理为出发点，研究了一种将正电压输入转为负电压输出的开关电容电路。由于开关电容的充放电特点，为确定电容时间常数，采用非交叠时钟控制信号避免了由于时钟交叠而造成的当电容充电还未完成即对下一级电容进行放电的现象。同时，参考功率MOS-FET的电容模型通过增大驱动电路的电流减小了开关管的上升延时，提高了开关动作的速度，使转换效率得到明显提高。此电路结构简单，性能优良，易于集成，可广泛应用于输出负电压的电源产品中。     

估计小波系数方差邻域大小的研究

利用小波变换去噪时小波系数方差的估计对去噪结果影响很大。自然图像小波分解后得到的系数在不同的分辨率中差异很大,所以利用邻域估计中心点方差时,不同分辨率应有不同大小的邻域。首先对在邻域中利用极大似然准则估计中心点方差进行分析,再结合自然图像小波分解后的系数在不同分辨率子带中,根据平稳性和重要性选择邻域的大小。最后进行去噪实验,并取得正交小波分解下理想的去噪性能。     

一种新的图像水印方案

目标区域是图像中视觉上最重要的部分。针对现有的水印算法很少考虑图像中确定的目标区域这一问题，提出了一种基于目标区域的水印方案(WIOR)。方案首先利用小波变换分析图像的目标特征，并依据图像的小波高频系数特征对其进行聚类，获得水印的嵌入域，在此嵌入域中，选择小波系数并对其进行量化调制来嵌入二值扩谱水印；同时，通过只在图像的局部区域内嵌入较少的水印信息来改善水印的隐蔽性。实验结果表明，该方案对于一类具有突出目标特征的图像具有较好的效果。嵌入的水印主要优势在于真正把水印嵌入图像的视觉重要部分，从而能有效地抵御剪切攻击，而且可以实现盲检测。